Mar. 27, 2013 — Zooplankton, small fish and squid spend hardly any time at the surface when there's a full moon. To protect themselves from their natural enemies, they hide deeper down in the water on bright nights, coming up to the surface under cover of darkness when there's a new moon instead. Scientists at the Max Planck Institute for Ornithology in Radolfzell discovered that this also influences the behaviour of swallow-tailed gulls (Creagrus furcatus), a unique nocturnal species of gull from the
They fitted the birds with loggers and wet/dry sensors which enabled them to see how much time the animals spent at sea at night. Their findings show that the birds' activity was greatest at new moon, in other words the time when the most prey was gathered at the surface of the water. The cycle of the moon therefore also influences the behaviour of seabirds.
The lunar cycle controls the behaviour of various animal species: owls, swallows and bats, for example, align their activity with the phase of the moon to maximise their hunting success. However, marine life is also affected by the moon. Many species of fish hide from their enemies in the depths of the sea during the daytime and only come up to the water's surface in the dark. Known as vertical migration, this phenomenon is additionally influenced by the lunar cycle. The fish thereby avoid swimming on the water's surface at full moon where they would be easy prey. Vertical migration is thus restricted on brighter nights and the animals remain at greater depths. At new moon, on the other hand, the organisms become active and migrate to the surface.
Yet also in the dark of night hunters lie in wait for them -- for instance the swallow-tailed gull Creagrus furcatus from the
Galapagos Islands. With eyes that are well adapted to the
dark, the gull can see fish below the water's surface even in low light
conditions and so does not need the moon as a source of light. Scientists from
the Max Planck Institute for Ornithology therefore wanted to find out what
effect the lunar cycle had on the hunting behaviour of the gulls.